1. Field of the Invention
This invention relates to an economical delivery system for the application of liquid dental materials, especially adhesive materials, during restorative dental treatments. More particularly, the invention pertains to a safe, easy to use application system wherein the adhesive materials are maintained in dental carpules which are designed to eliminate the possibility of inadvertent injection of the adhesive materials into tissue. Moreover, the system includes specialized structure for maintaining a bubble of protective gas within the carpules while at the same time insuring that tubular liquid application structure associated with the carpule remains in constant communication with the liquid within the carpule; in this manner, expression or leakage of the protective gas from the carpule is inhibited during use of the system.
2. Description of the Prior Art
Restorative dentistry is an evolving field wherein patients with damaged, diseased, disfigured or discolored teeth may have the teeth resurfaced or reconstructed to an optimum shape and appearance. In recent years, use of porcelain dental restorations has achieved a considerable degree of commercial success, particularly in view of the enhanced aesthetic effects which can be obtained using porcelain restorations. For example, porcelain restorations may be applied in the forms of crowns, inlays, or veneers.
In the application of porcelain veneers, practitioners often etch either the teeth to be restored or the undersides of the restorations (or both) using an acid solution. Further, use is often made of dentinal or enamel lining or adhesive materials in order to firmly bond the restorations to teeth. One such method which has achieved significant commercial acceptance is disclosed in U.S. Pat. No. 4,654,007 entitled "Porcelain Dental Restoration Method".
It has also been proposed in the past to employ adhesive materials such as pyromellitic dianhydride dimethacrylate (PMDM) for attachment of porcelain restorations. PMDM must be continually exposed to oxygen during storage and prior to use, else it will prematurely polymerize. By the same token, acidic surface conditioning etching solutions containing a combination of N-phenyl glycine (NPG) and HNO.sub.3, or alternatively phosphoric acid, used in conjunction with PMDM should be protected from the adverse affects of air prior to actual application. Accordingly, it has been suggested to package PMDM and associated acidic surface conditioning etching agents in respective dental carpules each containing a bubble of protective gas (oxygen in the case of PMDM, and an inert gas such as argon in the case of the surface conditioner etchant).
While use of carpules with protective gas bubbles would appear to represent a complete solution to the storage problem, a number of practical difficulties have arisen. First, the dental carpules heretofore employed for PMDM and surface conditioner etchant are of the standard size and shape heretofore used for injectable materials such as dental anesthetics. Such carpules are sized to fit within a conventional dental injection syringe found in every dentist's office. As can be appreciated, it would be hazardous indeed to supply PMDM and acidic surface conditioner etchants in these standard carpules, because of the real danger that the PMDM and/or surface conditioner etchant could be inadvertently injected using a conventional dental syringe. For this reason, packaging of PMDM and etchants in completely standard dental carpules has not been approved.
Furthermore, if standard dental carpules containing PMDM or surface conditioner etchant are employed with conventional dental syringes, there is a very real possibility that the protective gas bubbles within the carpules would be immediately ejected or expressed upon initial use. This stems from the fact that the dental syringes are provided with only very short membrane-puncturing tubular members designed to pass into the dental carpules to the minimum extent necessary to establish fluid communication between the carpules and the injection needles used with the syringe. As will be readily seen, use of long membrane-puncturing tubes would prevent full use of the anesthetic or other injectable material within the carpule.
Accordingly, there is a real and heretofore unsatisfied need in the art for an improved system particularly designed for precise application of liquid dental materials such as adhesives and etchants which are suitable for repeated use on a succession of patients while eliminating the possibility of inadvertent tissue injection and/or loss of protective gas.